Appy,
Thanks for the info!
From the Voltages you described, it appears that the secondary distribution systems are 4 wire Wye's [AKA 4 wire Star].
Also looks like the common conductor is used for a dual voltage system [230Y/400 3 phase 4 wire]. It seems to be bonded to Earth much the same way we do it here.
One thing came up while looking over this type of system is the problems related to arcing ground faults that are inherent with 4 wire Wye systems above 150 VAC to ground. In the US, it becomes a matter when the service's rating is 1000 amps, or more.
The use of Ground Fault Protecting type main breakers [or similar type of main disconnect] is done here. Ground fault limits are very high, as compared to the limits for personnel protection, plus they only monitor Line-to Ground faults, no overcurrent protection is done with these [except that of the main protecting device].
I'll keep the Techno Babble junk low here, but if you are curious about this, let me know.
Don't know if and where this might be used in your situations, so feel free to elaborate if you want to.
BTW: If there is only one Transformer with only two Primary feeder conductors to it, that would be, of course, a Single Phase system. This would be where you would find a center tapped transformer with some connection to that center tap - either a Neutral Conductor, or just a point for grounding.
This was the one I am curious about. If the transformer has the center tap grounded, that lowers the voltage to ground by 1/2 [half of the transformer's winding's potential]. If it's only grounded at the transformer and there is no physical wire coming to a service, which gets bonded to the metal enclosure and possibly grounded once again, that leaves a poor path for ground fault current. The path is in the dirt only.
I am almost completely positive that your systems are not done this way, but if they are please let me know.
The center tap and conductor from it to the service would not be used in any circuits.
If the 1 phase transformer was 230/460 VAC, then the center tap would be used as a typical Neutral Conductor, being part of circuits, along with the typical ground bonding stuff.
So you use 50Hz.. That's about the lowest frequency that is practical when multi use power distribution is concerned.
60 Hz is about the highest [which is what we use].
These Hz values are the best "Happy Medium" for plain old general use power, which is transmitted over a distance more than 25 miles and is to be used in high levels.
The Skin Effect, which greatly effects large conductors, is a little lower for the 50 Hz power. The trade off is a lower Synchronous Speed for the AC. This results in Transformer Cores and Coils that are a little larger. plus a little more lossier than their 60 Hz counterparts, plus general usage type Induction motors will have a max speed of 3,000 RPMs, as compared to 3,600 RPMs using 60 Hz.
25 Hz would be good to overcome Skin Effect, but would require large, lossy transformer cores - and Induction motors would max out at 1,500 RPMs. Not only that, but there would be a noticable flickering of lights when the sine waves crossed the Zero line.
400 Hz would improve the efficency of transformers, plus lights - along with giving a high speed to Induction Motors [24,000 RPMs], but the Skin Effect losses would be dramatically raised at this frequency. That's why 400 Hz is used on low to medium powered systems that are locally derived.
Just my $0.02
Scott SET